package com.lagou.sqlSession.impl;

import com.lagou.executor.impl.SimpleExecutor;
import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import com.lagou.sqlSession.SqlSession;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String statementId = className + "." + methodName;
                System.out.println("\n[mapper invoked] statementId=" + statementId);

                MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
                if (mappedStatement.isUpdate()) {
                    // ---------- 增删改 ----------
                    return update(statementId, args);

                } else {
                    // ---------- 查询 ----------
                    // 获取被调用方法的返回值类型
                    Type genericReturnType = method.getGenericReturnType();

                    // 根据返回类型是否有泛型来判断查集合还是单个对象
                    if (genericReturnType instanceof ParameterizedType) {
                        List<Object> objects = selectList(statementId, args);
                        return objects;
                    }
                    return selectOne(statementId, args);
                }
            }
        });

        return (T) proxyInstance;
    }

    @Override
    public <E> List<E> selectList(String statementId, Object... param) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, param);
        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
        List<Object> objects = selectList(statementId, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public int update(String statementId, Object... param) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, param);
    }
}
